Study on the Role of MgO in High‐Basicity Mold Flux for Ultrawide Slab Peritectic Steel

In order to explore the mechanism of MgO in CaO–SiO 2 ‐based high‐basicity mold flux for ultrawide slab peritectic steel, the microstructure of slag at 1300 °C is studied by in‐situ high‐temperature micro‐Raman spectrometer, and the mechanism of MgO causing the change of slag viscosity is analyzed. In addition, the effect of MgO on the melting and crystallization properties of mold fluxes is studied by using improved full‐field high‐temperature confocal microscope and other equipment. The results demonstrated that MgO facilitates the depolymerization of the complex network structure, thereby reducing the viscosity of the slag. However, once the MgO content exceeds 6 wt%, its impact on viscosity becomes negligible. MgO significantly influences the break temperature ( T br ), melting point, and initial crystallization temperature ( T C ) of the mold flux. When it is below 7 wt%, T C decreases by 17 °C for every 1 wt% increase in MgO. However, once it surpasses 7 wt%, T C ceases to decrease and instead begins to rise. Similar trends are observed for the melting point and average crystallization rate, with a critical MgO content of 6 wt%. Moreover, under two different cooling rate conditions, T C decreases by 12.38 and 13.38 °C for each 1 wt% increase in MgO, respectively.